The present invention relates to surgical treatment procedures and instruments, and particularly utilizing laser radiation for the removal of tooth and gum tissue.
In dental procedures, it is frequently desirable to remove portions of tooth enamel and dentin, and in certain cases, portions of gum tissue, in an accurately controlled manner and there has been a growing interest in the use of laser radiation for performing such procedures. The use of laser radiation is attractive because, particularly with the aid of optical fibers, such radiation can be focused to a very small area and is thus compatible with the dimensional scale of dental procedures. Moreover, laser radiation procedures can be performed without recourse to an anesthetic.
While a number of devices of this type have been proposed, they have not proven to be of practical use notably because even the most effective of those devices already proposed are useful only under limited and very precisely defined conditions.
The enamel and dentin of a tooth include, as one component, hydroxyapatite, which is in amorphous form in the dentin and crystalline form in the enamel. These portions of a tooth additionally include organic tissues and water, but have no vascular system. Healthy dentin is in mineralized form, while dentin which has experienced decay is in demineralized form. Dentin has a relatively high percentage of organic tissue, around 40 percent, and also a high percentage of water. These percentages increase considerably in decayed dentin.
Tooth pulp and the gum surrounding the teeth consist of vascularized organic tissue containing both hemoglobin and water. Each of these components has a different response to laser radiation.
Thus, it has been found, that hydroxyapatite absorbs laser radiation in the wavelength ranges of 9-11 .mu., such as produced by CO.sub.2 lasers, and also in the wavelength range 0.5-1.06 .mu., which includes the wavelength that can be produced by a YAG laser.
The laser radiation absorption by the various parts of a tooth at various wavelengths is influenced by the absorption of the radiation energy by the water component thereof. The greater the absorption by water, the less energy is available for absorption by the other components. Since the wavelengths of the radiation emitted by CO.sub.2 lasers is absorbed to a large extent by water, this radiation has minimal cutting effect on enamel or dentin, and less of a cutting effect on mineralized dentin than on demineralized dentin.
On the other hand, it has been found that radiation at a wavelength of 1.06 .mu. is absorbed to a lesser degree by water, and therefore has a greater effect on mineralized tissues. Laser radiation at a wavelength of 0.532 .mu. is not absorbed at all by water and can be effective on mineralized tissues if a sufficiently high, and thus dangerous, power level is employed.
As regards vascularized tissues, radiation at the wavelengths emitted by CO.sub.2 lasers has an effective cutting action because of its absorption by water, while radiation at a wavelength of 1.06 .mu. does not have any effect, and radiation at a wavelength of 0.532 .mu. has a cutting effect on soft tissues because, although not absorbed by water, it is well absorbed by hemoglobin.
While a particular wavelength may inherently have a cutting effect on enamel or dentin, it has been found that the practical utilization of radiation at such a wavelength for dental procedures is highly dependent on the form in which the radiation is applied, with respect to energy level, pulse duration and repetition rate. Specifically, efforts to apply such radiation in the form of high energy pulses of short duration have been found to produce a highly localized temperature increase, resulting in differential thermal expansion which can cause mechanical damage to the tooth as well as vascular damage to pulp tissue. Conversely, low energy pulses of long duration cause a more widespread heating of the tooth which results in patient discomfort as well as pulp damage due to heating.